1. Technical Field
The invention generally relates to screws, particularly to self-tapping screws.
2. Related Art
Conventional screws are made of metallic materials. A screw is composed of a head, a rod extending from the head and a thread around the rod. To accomplish the effect of anti-loosen, a traditional approach is to form an expanded portion at an end of the thread.
However, the traditional anti-loosen screw is not good enough in aspects of tightness and toughness.